Patients claim lives are being put "at risk" after it emerged some women are waiting six times the two-week target to get their smear test results.
Cervical screening samples are usually taken at GP clinics before being sent off to laboratories for testing.
Samples from the eastern region are taking up to 12 weeks to process by Cambridge University Hospitals.
NHS England said it is "working closely" with screening labs to "free up additional capacity".
One of those affected is lawyer Alexandra Borrett, who lives in Brantham on the Essex/Suffolk border.
She has been waiting more than 10 weeks for her results to come back from Cambridge University Hospitals.
She said: "My doctor's surgery tells me there is a delay with the testing and I just have to wait and they have no idea when the results will be back.
"This is unacceptable.
"I am a little bit anxious, but I am more worried that it is not just me and whenever I call my GP surgery they tell me I am the third or fourth person to call that day, and that is just one surgery, so there must be thousands of women awaiting their results and some of us, statistically, must have signs of cancer.
"My friends in other parts of the country are getting their results within two weeks, I don't see why women in this area should have their lives put at risk."
A second woman, from Chelmsford in Essex, who asked not to be identified, said she waited eight weeks for her result.
"When I asked why it had taken so long to get the result I was told there was such a high volume of cases," she said.
Cambridge University Hospitals provides screening for patients living in parts of Cambridgeshire, Essex, Hertfordshire and Suffolk.
Dr Michael Eden, the cervical cytology network clinical lead at Cambridge University Hospitals, said routine screening was currently taking up to 12 weeks because of "current staff shortages".
He added: "We would like to reassure women that if they go to their GP with symptoms that cause concern, and they are due or overdue for screening, their test will be marked as urgent and the results turned around rapidly."
Dr Eden said a new screening system - called human papilloma virus (HPV) primary screening - will be rolled out in 2020, which, he said, "will increase regional and national capacity".
Shylaja Thomas, screening and immunisations lead for NHS England (Midlands and East) said: "We are working closely with the screening service providers to free up additional capacity so that tests can be processed more quickly."
Robert Music, chief executive of Jo's Cervical Cancer Trust, said: "Waiting for results can already be a very anxious time and having to wait up to four months may mean additional worry."